Boolean modifier not working and also material not applied
You can expect that behaviour of boolean modifier, if you try to cut in ngons (face with more then 4 vertices). Blender is smart enough to cut it smoothly in other parts of the mesh, but in this particular part, something went wrong. Fortunately boolean works, but not in perfect way. Here you'll see how to fix that and that you can apply material to your mesh without problem.What I didn't show in this short .gif is that you should always have normals pointing outside so you need on all your meshes in edit mode, with all faces selected press CTRL+N to calculate them.